Oil viscosity has a direct effect on engine friction which in turn affects engine torque output and idle speed. Therefore engine friction should be estimated or assumed by many parts of the engine control strategy including idle speed control and electronic throttle control. Oil viscosity also affects oil pressure, which in turn affects systems like VCT (variable camshaft timing) which rely on oil pressure to operate.
For traditional engine oils, viscosity changes dramatically as a function of temperature (i.e., a low viscosity index). New oils are being developed that have much higher viscosity index, so their viscosity changes much less with temperature.
Some engine control strategies include temperature modifiers which help compensate for changes in oil viscosity. For example, at low temperature, and higher viscosity, a greater throttle opening (higher airflow) is used to achieve a desired idle speed or engine output torque.
The inventors herein have recognized that these temperature modifiers may cause undesired operation if the engine is refilled with oil having a viscosity index which is significantly different than the manufacturer's recommendation. For example, temperature modifiers designed for manufacturer recommended high viscosity index oil will not change idle throttle openings much at low temperature. If the engine is refilled with low viscosity index oil, the idle speed at low temperatures will be lower than intended, and the engine may stall.
The inventors have solved these issues by a new control strategy which detects actual oil viscosity and/or viscosity index and controls the engine appropriately. In one aspect, a new control method comprises: after engine shutdown, learning engine oil viscosity based on time to drain the oil back into an engine sump and oil temperature during the draining; and correcting an engine operating parameter based on the learned oil viscosity. In a particular aspect of the disclosure the engine operating parameter is a throttle plate and the throttle plate is commanded to a desired throttle angle, or position, to allow a desired amount of air to be inducted into the engine, and the desired throttle angle is corrected based upon the learned oil viscosity. The throttle plate is commanded to an initial throttle position to achieve a desired engine idle speed. In another application the throttle plate is commanded to an initial position to provide a desired torque output of the engine. Thus, the technical effect is achieved by these actions.
In another aspect of the disclosure, the inventors have provided a method which learns oil viscosity index and controls the engine appropriately. In particular, the method comprises: after engine shutdown, learning oil viscosity of engine oil based on temperature of the oil and time to drain the oil back into an engine sump; after at least two of the engine shutdowns at different temperatures, learning viscosity index of the oil from at least two of the learned oil viscosities; and correcting an engine operating parameter based on current temperature of the oil and the viscosity index of the oil. In a more specific example, the operating parameter of the engine comprises a throttle position or angle of a throttle plate controlling an amount of air inducted into the engine. And, the throttle plate is commanded to a desired throttle position to allow a desired amount of air to be inducted into the engine and said desired throttle position is corrected based upon said viscosity index and said current temperature
In still another example oil viscosity index is learned and it in turn is used to correct a throttle position for idle speed control. More specifically the control method comprises: after engine shutdown, learning oil viscosity of engine oil based on temperature of the oil and time to drain the oil back into an engine sump; after at least two of the engine shutdowns at different temperatures, learning viscosity index of the oil from at least two of the learned oil viscosities; controlling engine idle speed by first determining an initial throttle position based on a desired idle speed and an assumed oil viscosity; and correcting the initial throttle position based upon the learned viscosity index and present oil temperature. The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.